Due to advantageous features such as thin profile, light weight, and low power consumption, liquid crystal display devices are used in a wide range of fields including mobile communication systems, monitors, and large televisions. Various performances are required in these fields, and various display modes have been developed. As the fundamental structure and principle, these liquid crystal display devices include a pair of substrates for interposing a liquid crystal layer therebetween; and control the transmission/shielding of light (on/off of the display) by appropriately applying a voltage to electrodes disposed on the liquid crystal layer side of at least one of the pair of substrates, and by controlling the alignment direction of liquid crystal molecules in the liquid crystal layer, thus achieving liquid crystal displays.
Examples of the display modes of recent liquid crystal display devices include a vertical alignment (VA) mode in which liquid crystal molecules having negative anisotropy of dielectric constant are aligned vertically to the substrate surface; and an in-plane switching (IPS) mode and a fringe field switching (FFS) mode in which liquid crystal molecules having positive or negative anisotropy of dielectric constant are aligned horizontally to the substrate surface, and a horizontal electric field is applied to the liquid crystal layer.
Herein, as a method of obtaining a high-luminance and high-speed response liquid crystal display device, alignment stabilization techniques using a polymer (hereinafter, also referred to as “polymer sustained (PS) treatment”) have been suggested (for example, see Patent Literatures 1 to 9). Among these, according to pre-tilt angle imparting techniques using a polymer (hereinafter, also referred to as “polymer sustained alignment (PSA) technique”), polymerizable components such as a polymerizable monomer and a polymerizable oligomer are mixed to obtain a liquid crystal composition, which is then sealed between the substrates; a voltage is applied between the substrates to tilt liquid crystal molecules; and the monomer is polymerized to form a polymer, with the liquid crystal molecules being tilted. This results in liquid crystal molecules that are tilted at a certain pre-tilt angle even after the voltage application is stopped, and thus the liquid crystal molecules can be aligned in a certain direction. Materials that are polymerizable by heat, light (ultraviolet light), and the like are selected as monomers to form a polymer.
According to another disclosed document, for example, one substrate was subjected to photo-alignment treatment and PS treatment and the other substrate was subjected to rubbing treatment, in a liquid crystal display device; and the influence of hysteresis and the like on the monomer concentration for PS treatment in liquid crystal were investigated (for example, see Non-Patent Literature 1).